Lactobacillus acidophilus is a Gram-positive, rod-shaped, non-spore forming, homofermentative bacterium that is a normal inhabitant of the gastrointestinal and genitourinary tracts. Since its original isolation by Moro (1900) from infant feces, the “acid loving” organism has been found in the intestinal tract of humans, breast fed infants, and persons consuming high milk-, lactose-, or dextrin diets. Historically, L. acidophilus is the Lactobacillus species most often implicated as an intestinal probiotic capable of eliciting beneficial effects on the microflora of the gastrointestinal tract (Klaenhammer, T. R., and W. M. Russell. 2000. Species of the Lactobacillus acidophilus complex. Encyclopedia of Food Microbiology, Volume 2, pp 1151-1157. Robinson, R. K, Batt, C., and Patel, P. D (eds). Academic Press, San Diego). L. acidophilus can ferment hexoses, including lactose and more complex oligosaccharides (Kaplan and Hutkins (2000) Appl. Environ. Microbiol. 66, 2682-2684) to produce lactic acid and lower the pH of the environment where the organism is cultured. Acidified environments (e.g. food, vagina, and regions within the gastrointestinal tract) can interfere with the growth of undesirable bacteria, pathogens, and yeasts. The organism is well known for its acid tolerance, survival in cultured dairy products, and viability during passage through the stomach and gastrointestinal tract. Lactobacilli and other commensal bacteria, some of which are considered as probiotic bacteria that “favor life,” have been studied extensively for their effects on human health, particularly in the prevention or treatment of enteric infections, diarrheal disease, prevention of cancer, and stimulation of the immune system.